Recently there have been made considerable efforts to impart to the novel superconductor (s.c.) ceramic materials some metallic properties to improve the mechanical properties of these s.c.. Properties such as machineability, moldability, metal wetting properties (soldering) may improve considerably by preparing a composite material of a s.c. and metal. Some of the attempts reported in the literature to achieve such properties are characterized by a random mixing of metal and s.c. powder to form a composite (1,2) which is subsequently sintered at high temperature. To create an interpenetrating network of metal in the composite, above the percolation threshold, a considerable volume fraction of the metal is necessary. According to the present invention, a new, non-random approach for the preparation of s.c. metal composite is presented. These new materials comprise micro grains of a ceramic superconductor (such as Y Ba.sub.2 Cu.sub.3 O.sub.7) which are coated with a thin metal film and subsequently sintered at high temperature (450.degree. C.-900.degree. C.) to form a superconducting composite. Already at a very low metal loading of about 5% by volume, far below the percolation limit for the metallic component in random mixtures, a continuous honeycomb-like structure is created in which the grains of the ceramic material are nested.
Ceramics of the type QBa.sub.2 Cu.sub.7-x where Q designates yttrium or europium essentially of the prescovite structure can be obtained in the form of ceramic pellets when fired at an appropriate elevated temperature, exhibit both the Meissner effect and a transition to a zero-resistivity state when cooled to a temperature below T.sub.c -94.degree. K. With the yttrium compound the firing ought to be at about 940.degree. C. When such pellets are crushed to a powder and reconstituted to a pellet by the applicaltion of pressure at ambient temperature, the Meissner effect is recovered whereas the transition to zero-resistivity state is lost. The overall conductivity behavior as function of temperature of such reconstituted pellets is that of a semiconductor. It is of great practical importance to be able to convert such materials to superconducting products which can be machined, rolled and soldered. It is furthermore of extreme practical importance to be able to provide such materials in a form which is flexible and not brittle.